This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A304994 #11 May 26 2018 16:48:03
%S A304994 1,4,6976,8,15
%N A304994 a(n) is the smallest number k such that sigma(k + n) = sigma(k) - n, or -1 if no such number exists.
%C A304994 Further terms of the sequence: a(5) > 10^9 (if it exists), a(6) = 35, a(7) = 16, a(8) = 39, a(10) = 51, a(12) = 95, a(14) = 831, a(15) = 32, a(16) = 45, a(18) = 88, a(19) = 36, a(20) = 63, a(21) = 50, a(22) = 222, a(24) = 135, a(26) = 37888, a(28) = 96, a(30) = 284, a(32) = 117, a(34) = 354, a(36) = 175, a(37) = 1089, a(38) = 84, a(40) = 153, a(42) = 176, a(44) = 3893, a(46) = 267, a(48) = 210. - _Daniel Suteu_, May 25 2018
%C A304994 a(5) > 3*10^12, if it exists. - _Giovanni Resta_, May 26 2018
%e A304994 sigma(4+1) - sigma(4) = -1, so a(1) = 4, since this does not happen for x < 4.
%e A304994 sigma(8+3) - sigma(8) = -3, so a(3) = 8, since this does not happen for x < 8.
%o A304994 (PARI) a(n) = {my(k=1); while(sigma(k+n) != sigma(k) - n, k++); k;}
%Y A304994 Cf. A000203, A015886.
%K A304994 nonn,more
%O A304994 0,2
%A A304994 _Michel Marcus_, May 23 2018